Cyclic germanium compounds and applications thereof

ABSTRACT

The present disclosure provides a new series of compounds exhibiting high fluorescence quantum yields in the solid state. In one embodiment, the compounds include a series of 2,3,4,5-tetraphenylgermoles with the same or different 1,1-substituents. In another embodiment, substituted germafluorenes, germa-fluoresceins/rhodamines, and germapins are described. These germanium heterocycles possess ideal photophysical and thermostability properties, which makes them excellent candidates for chemical or biological sensors, host materials for electroluminescent devices and solar cells, and emissive and/or electron-transport layer components in organic light emitting diode devices.

CROSS-REFERENCE TO RELATED APPLICATIONS

This divisional application claims priority to U.S. patent applicationSer. No. 14/406,777, filed on Dec. 10, 2014, which is a National StageEntry of International Application Number PCT/US2013/045201, filed onJun. 11, 2013, U.S. Provisional Patent Application No. 61/690,456, filedon Jun. 26, 2012, and U.S. Provisional Patent Application No.61/689,723, filed on Jun. 11, 2012, the disclosures of which are herebyexpressly incorporated by reference in their entireties.

GRANT STATEMENT

This invention was made with Government support under the Grant No.CHE-0719380 awarded by the National Science Foundation. The Governmenthas certain rights in the invention.

FIELD OF THE DISCLOSURE

The present disclosure relates to compounds for use as luminescentmaterials and, most specifically, as luminescent materials that exhibithigh fluorescence quantum yields in the solid state. The compounds areideal candidates for a variety of applications, including for use aselectron-transporting or emissive layers in semiconducting andelectronic devices and as chemical and biological sensors. In oneparticular embodiment, the compounds are used as chemosensors for thedetection of volatile organic compounds (VOCs) such as acetone.

BACKGROUND OF DISCLOSURE

For the past few decades, the development of efficient luminescentmaterials, having desirable optoelectronic properties, has been a topicof great interest. The development of efficient luminescent materials,however, has been hindered by problems associated withaggregation-caused quenching of light emission which is notorious forrendering luminophors ineffective for solid state applications,particularly those involving electroluminescent (EL) devices. In orderfor luminescent materials to have practical applications aselectron-transporting or emissive layers as thin films in semiconductingand electronic devices, a luminophor should exhibit high fluorescencequantum yield (Φ_(F)) in the solid state. Many organic fluorophoresexperience aggregation-caused quenching (ACQ) of light emission insolution as well as the solid state as a result of interactions withneighboring fluorophores which promote the formation of delocalizedexcitons or excimers which decay non-radiatively. As a result, lowconcentrations of the fluorophore molecule must be used in order tominimize contact between adjacent molecules to mitigate the ACQ effectresulting in decreased sensitivity and reliability of the fluorescentsignal. A logical approach to alleviating the problems associated withACQ would be to develop luminophors whose aggregates fluoresce morestrongly than their solutions. Identification of two photoluminescenceprocesses, aggregation-induced emission (AIE) and aggregation-inducedemission enhancement (AIEE), may now allow development of highlyefficient solid state fluorescence. In AIE, a non-emissive chromophoreis induced to emit light by the formation of aggregates while the lightemission of an AIEE molecule is significantly enhanced once aggregationoccurs.

Silacyclopentadienes, or siloles (FIG. 1, M=Si), are a class ofmolecules that have been previously extensively developed for theirpotential application in organic electronics, particularly in flexiblelighting and display panels. One of the qualities responsible for theintense interest in siloles is the high electron affinity that thesecyclic molecules exhibit. Such large electron affinities can beattributed to a low lying LUMO which arises from σ*-π* conjugation thatresults from the interaction between the π* orbital of the butadienesegment and the σ* orbital associated with the two exocyclic bonds onthe silicon center. The large electron affinity of the siloles resultsin another favorable feature, high electron mobility, a desirableattribute that continues to present challenges in the design of highlyefficient organic electronic devices. There are many silole derivativesthat have been reported to be good electron transporters with electronmobilities that are two orders of magnitude higher thantris(8-hydroxyquinolinato)aluminum (Alq₃). Alq₃ is a commonly usedelectron-transport (ET) material for organic light-emitting diodes(OLEDs).

Siloles have demonstrated high photoluminescence (PL) quantum yields asboth amorphous and crystalline solids which can be attributed to theunique photophysical property of aggregation-induced emission (AIE). Asa result of the steric repulsions between the peripheral arylsubstituents on the core ring, intramolecular rotations of thesubstituents are restricted causing the substituents on the silole coreto assume a highly twisted conformation that persists in solution aswell as the solid state. Restriction of intramolecular rotations of theperipheral substituents effectively blocks non-radiative relaxationchannels and imparts non-planarity, rendering the distance betweenadjacent silole molecules too long for conventional π-π stackinginteractions (˜3-4 Å) that typically quench luminogens in the solid andcrystalline phases. This mechanism is referred to as restrictedintramolecular rotation (RIR) and is the accepted cause of the AIEphenomenon. RIR so effectively deactivates the avenues that result innon-radiative emission that siloles strongly emit light in the solid andcrystalline phases, such as aggregated suspensions in solvent-watermixtures.

The AIE effect has now been identified in other luminogens with similarstructural features including germoles, the heavier Group 14 congener ofsiloles (FIG. 1, M=Ge). Although germoles emit more efficiently insolution than siloles, their solutions are still only weakly emissive.The increased efficiency in solution, however, does not diminish thesignificant AIE effect that is exhibited by germoles in the solid stateor when aggregated in solvent-water mixtures. Germoles, like siloles,are soluble in a variety of common organic solvents, but insoluble inwater.

To date, relatively little has been published on the PL of germoles,despite published evidence of the similarities between siloles andgermoles. In addition to exhibiting the AIE effect, parallels betweenthe electronic structure and photophysical properties of the twometalloles can be seen by the similarities in the UV-vis absorption andfluorescence profiles, electrochemical data, and ab initio calculationsof HOMO and LUMO energy levels. Such studies indicate comparable σ*(Si—R) and σ* (Ge—R) orbitals as well low lying LUMO energy levels,suggesting that the differences in the electronic structures ofgermanium and silicon analogs are relatively minimal despite theslightly larger size of the germanium atom. This is in contrast to theattributes that would be gleaned from the low lying LUMO in stannoleswhich are diminished by significantly less efficient σ*-π* conjugationthat results from a greater orbital mismatch as well as elongated bonddistances between the larger 5p_(z) σ* orbital of tin and the 2p_(z) π*orbital of the carbons of the butadiene.

Therefore, there is a need to develop a series of compounds containing agermanium ring core, and in particular, germoles, exhibiting intensefluoresce quantum yields as aggregates in solution or in the solid stateto be employed in light-emitting devices and luminescent sensors.

SUMMARY OF THE DISCLOSURE

The present disclosure provides a new series of luminescent compoundscontaining a germanium ring core. In particularly suitable embodiments,the compounds are substituted germoles, substituted germafluorenes,substituted germa-fluoresceins or germa-rhodamines, or substitutedgermapins, exhibiting high fluorescence quantum yields in the solidstate.

Accordingly, in one embodiment, the compounds are a series of2,3,4,5-tetraphenylgermoles with same or different 1,1-substituents,which may have the formula (I)

wherein R₁ and R₂ may be independently selected from optionallysubstituted aryl, optionally substituted heteroaryl, or optionallysubstituted alkynyl.

In another embodiment, the compounds are a series of substitutedgermafluorenes having the general formula (II)

wherein R₁ and R₂ may be independently selected from the groupconsisting of aryl, alkyl, halide, alkynyl, and asymmetric derivativesthereof with two different groups at the Ge-center; wherein R₃ and R₆may be independently selected from the group consisting of Y and

wherein R₄ and R₅ may be independently selected from the groupconsisting of OCH₃ and Y; andwherein Y is H,

wherein Z is F, CH₃, or OCH₃;

wherein X is H, CF₃, OPh, CH₃, Ph, OCH₃ or OCF₃; or

wherein R is aryl, alkenyl or alkynyl.

In yet another embodiment, the compounds are substitutedgerma-fluoresceins or germa-rhodamines having the general formula (III)

wherein R₁ and R₂ may be independently selected from the groupconsisting of aryl, alkyl, halide, alkynyl, and asymmetric derivativesthereof with two different groups at the Ge-center; wherein R₄ and R₇may be independently selected from the group consisting of ═O, —OH, andOSi(CH₃)₂[C(CH₃)₃] hydroxyl or carbonyl amine and ether derivatives;wherein R₅ and R₆ are H; and,wherein R₃ is Y, ═O, C₆H₅, p-CH₃C₆H₅, p-CH₃OC₆H₅ or

wherein Y is

wherein Z is F, CH₃ or OCH₃;

wherein X═CF₃, OPh, CH₃, Ph, OCH₃ or OCF₃;

wherein NR₂═NH₂, NMe₂ or NEt₂ and Z=Me, CO₂H, C(═O)H, or CO₂Me;

wherein R is alkyl and Z=Me, CO₂H, C(═O)H, or CO₂Me; or,

wherein R is alkyl or H.

In another embodiment, the compounds are substituted germapins havingthe general formula (IV)

wherein R₁ and R₂ may be independently selected from the groupconsisting of aryl, alkyl, halide, alkynyl, and asymmetric derivativesthereof with two different groups at the Ge-center;wherein R₃ and R₆ may be independently selected from the groupconsisting of H, Cl, Ar, Y and

wherein R₄ and R₅ may be independently selected from the groupconsisting of H, aryl, I, Br, Y or

andwherein Y is

wherein Z is F, CH₃ or OCH₃;

wherein X is CF₃, OPh, CH₃, Ph, OCH₃ or OCF₃; or

wherein R is aryl, alkenyl or alkynyl.

The compounds of the present disclosure with their ideal photophysicaland thermostability properties may make them excellent candidates forchemical or biological sensors, host materials for electroluminescentdevices, solar cells, and light-emitting materials in organic lightemitting diode devices (OLEDs).

According to one particular embodiment of the present disclosure,germoles may be employed as coating materials on thin layerchromatography (TLC) plates for chemical or biological sensing (such asdetection of organic vapor compounds).

According to another embodiment of the present disclosure, germolesgermafluorenes, germa-fluoresceins/germa-rhodamines, and germapins maybe tuned to develop blue, green, or the more rare red light-emittingmaterials, which may be employed as the emissive and/orelectron-transport layer components in organic light emitting diodedevices (OLEDs). In another embodiment of the present disclosure, thegermafluoroenes may be used as a reagent to stain/detect subcellularorganelles in cell imaging applications (e.g., staining of themitochondria).

DESCRIPTION OF DRAWINGS

FIG. 1 is the basic metallole structure, M=Si, silole, M-Ge, germole;2,3,4,5=C.

FIG. 2 illustrates the synthesis scheme for germole compounds of thepresent disclosure according to one embodiment of the presentdisclosure.

FIG. 3A shows the selected bond distances (A), angles (deg), andtorsions (deg) for item 8 in FIG. 2. Thermal ellipsoids are shown at the50% probability level: Ge1-C30=1.890(2), Ge1-C39=1.897(2),Ge1-C2=1.954(1), Ge1-05=1.940(2), C2-C3=1.362(2), C3-C4=1.512(2);C2-Ge1-C5=91.83(6), Ge1-C2-C3=106.2(1), Ge1-C5-C4=105.8(1),C2-C3-C4=117.5(1), C3-C4-C5=1186(1), C30-Ge1-C39=105.68(7);Ge1-C2-C24-C25=36.5(2), Ge1-C5-C6-C7=30.3(2), C2-C3-C18-C19=−113.9(2),C5-C4-C12-C13=61.8(2).

FIG. 3B shows the selected bond distances (A), angles (deg), andtorsions (deg) for item 12 from FIG. 2. Thermal ellipsoids are shown atthe 50% probability level and the hydrogen atoms and the disorder onitem 12 from FIG. 2 have been omitted for clarity: Ge1-C50=1.929(2),Ge1-C52=1.940(3), C49-C51=1.516(4), C50-C51=1.349(4), Ge1-C54=1.897(4),Ge1-C56=1.904(4), P2-C53=1.774(4), P3-C55=1.74(1); C50-Ge1-C52=91.5(1),Ge1-C50-C51=106.6(2), C50-C51-C49=117.9(3), C51-C49-C52=117.3(3),C54-Ge1-C56=105.5(1); Ge1-C50-C47-C46=−48.7(4),Ge1-C52-C29-C30=−35.7(4), C52-C49-C34-C35=−56.7(5).

FIG. 4 includes the absorption spectra for the methylene chloridesolutions of germoles 2 and 4 from FIG. 2, which represent the range ofthe UV absorption maxima.

FIG. 5A shows the PL spectra for 0.01 mM of item 2 from FIG. 2 in pureacetone and acetone-water mixtures at room temperature (λ_(ex)=370 nm);FIG. 5B is a photo of the solutions of item 2 from FIG. 2 in pureacetone (far left) and acetone-water mixtures (40%, 50%, 60%, 70%, 80%,and 90% respectively) which correlates with the graph of the PL spectra.

FIG. 6 illustrates the quantum yield of item 2 from FIG. 2 vs. the watercontent of the mixed acetone-water systems.

FIG. 7 illustrates the absorption spectra of 0.01 mM of item 2 from FIG.2 in the mixed acetone-water solvent systems.

FIGS. 8A to 8C are TEM images of item 2 from FIG. 2. TEM images of item2 from FIG. 2 illustrate the small aggregate clusters (A) and largeraggregate clusters (B) that were observed in the water-acetone mixturecontaining 90% water; the electron diffraction pattern (C) exhibited byaggregates in the 10% water-90% acetone mixture.

FIGS. 9A to 9C are photos of the TLC plates of item 8 from FIG. 2: (A)prior to solvent exposure, (B) after exposure, and (C) after the solventevaporated.

FIGS. 10A and 10B illustrate the packing arrangement of crystalline item8 from FIG. 2: (A) showing the intermolecular distance between twomolecules of 8 (6.9 Å) at the 3,4-diphenyl substituents; (B) showing theinterplane separation between two molecules of item 8 from FIG. 2 andthe two shortest C—H-π hydrogen-bonding interactions of 3.0 and 2.7 Å.

FIG. 11 illustrates an exemplary synthesis scheme for germole compoundsof the present disclosure according to one embodiment of the presentdisclosure.

FIG. 12 illustrates an exemplary synthesis scheme for germafluorenecompounds of the present disclosure.

FIGS. 13A-D illustrate a comparison of the fluorescence between9,10-diphenylanthrancene (ca. 1×10⁻³ M) (A) and decreasingconcentrations of 2,7-bis((trifluoromethyl)-ethynyl)phenyl)germafluorene 1×10⁻³ M (B), 1×10⁻⁴ M (C), and 1×10⁻⁵ M (d) in CH₃CN.

FIGS. 14A-C illustrate crystals of2,7-bis((trifluoromethyl)-ethynyl)phenyl)germafluorene under ambientlight (A) and UV light (B) and fluorescence of the thin film (C).

FIG. 15 depicts the crystal structure of one exemplary germafluorene ofthe present disclosure.

FIG. 16 illustrates an exemplary synthesis scheme for germa-fluoresceinand germa-rhodamine compounds of the present disclosure.

FIG. 17 illustrates an exemplary synthesis scheme for germapin compoundsof the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSURE

The present disclosure provides several new classes of luminescentcompounds containing a cyclic germanium core. Specifically, thecompounds are separated into four groups: (I) germoles, (II)germafluorenes, (III) germa-rhodamines or germa-fluoresceins, and (IV)germapins with the following respective formulas

The present disclosure also provides synthetic schemes for the inventivecompounds.

Germoles

In one aspect, the present disclosure is directed to a new series ofgermoles as luminophore materials with desirable thermal andmorphological properties, especially the unique photophysical propertyof aggregation-induced emission (AIE). The research endeavor was todevise ways to introduce substituents at the 1,1-positions (FIG. 1) thatwere different from the traditional phenyl or methyl groups that aretypically utilized for germoles. The present disclosure is directed totwo distinct classes within this series: germoles possessing the sametwo substituents (symmetrical) and those with different substituents(unsymmetrical) at the germanium center. The preparation of theseclasses is disclosed.

In one embodiment, the germoles are a series of2,3,4,5-tetraphenylgermoles with same (symmetrical) or different(unsymmetrical) 1,1-substituents, which may have the formula (I)

wherein R₁ and R₂ may be independently selected from optionallysubstituted aryl, optionally substituted heteroaryl, or optionallysubstituted alkynyl. According to one embodiment of the disclosure, R₁and R₂ may be selected independently from the group consisting of

wherein X═H, CF₃, OCF₃,

CH₃, OCH₃, Ph, OPh

and derivatives thereof.

In one embodiment of the present disclosure, R₁ and R₂ are each

In another embodiment of the present disclosure, R₁ and R₂ are each

In yet another embodiment of the present disclosure, R₁ and R₂ are each

In still another embodiment of the present disclosure, R₁ and R₂ areeach

In still another embodiment, the aryl is optionally substituted phenyl.

As used herein, “aryl” refers to a radical of a monocyclic or polycyclic(e.g., bicyclic or tricyclic) 4n+2 aromatic ring system (e.g., having 6,10, or 14 electrons shared in a cyclic array) having 6-14 ring carbonatoms and zero heteroatoms provided in the aromatic ring system (“C6-14aryl”). In some embodiments, an aryl group has 6 ring carbon atoms (“C6aryl”; e.g., phenyl). In some embodiments, an aryl group has 10 ringcarbon atoms (“C10 aryl”; e.g., naphthyl such as 1-naphthyl and2-naphthyl). In some embodiments, an aryl group has 14 ring carbon atoms(“C14 aryl”; e.g., anthracyl).

Exemplary substituents include groups that contain a heteroatom (such asnitrogen, oxygen, silicon, phosphorous, boron, sulfur, or a halogenatom), halogen (e.g., chlorine, bromine, fluorine, or iodine), aheterocycle, alkoxy, alkenoxy, alkynoxy, aryloxy, hydroxy, protectedhydroxy, keto, acyl, acyloxy, nitro, amino, amido, nitro, cyano, thiol,ketals, acetals, esters and ethers. In one embodiment, the compoundscomprise “heteroaryls.”

As used herein, “alkyl” refers to a radical of a straight-chain orbranched saturated hydrocarbon group having from, in some embodiments, 1to 4 carbon atoms (“C1-4 alkyl”), and in other embodiments 1 to 22carbon atoms (“C1-22 alkyl”). In some embodiments, an alkyl group has 1to 3 carbon atoms (“C1-3 alkyl”). In some embodiments, an alkyl grouphas 1 to 2 carbon atoms (“C1-2 alkyl”). In some embodiments, an alkylgroup has 1 carbon atom (“C1 alkyl”). In some embodiments, an alkylgroup has 2 to 4 carbon atom (“C2-4 alkyl”). In yet other embodiments,an alkyl group has 1 to 21 carbon atoms (“C1-21 alkyl”), 1 to 20 carbonatoms (“C1-20 alkyl”), 1 to 15 carbon atoms (“C1-15 alkyl”), 1 to 10carbon atoms (“C1-10 alkyl”), etc. Examples of such alkyl groups includemethyl (C1), ethyl (C2), n-propyl (C3), isopropyl (C3), n-butyl (C4),tert-butyl (C4), sec-butyl (C4), iso-butyl (C4), pentyl (C5), and thelike.

As used herein, “alkenyl” or “alkene” refers to a radical of astraight-chain or branched hydrocarbon group having from, in someembodiments, 2 to 4 carbon atoms (“C2-4 alkenyl”), and in otherembodiments 2 to 22 carbon atoms (“C2-22 alkenyl”), and one or morecarbon-carbon double bonds. In some embodiments, an alkenyl group has 2to 3 carbon atoms (“C2-3 alkenyl”). In some embodiments, an alkenylgroup has 2 carbon atoms (“C2 alkenyl”). In yet other embodiments, analkenyl group has 2 to 21 carbon atoms (“C2-21 alkenyl”), 2 to 20 carbonatoms (“C2-20 alkenyl”), 2 to 15 carbon atoms (“C2-15 alkenyl”), 2 to 10carbon atoms (“C2-10 alkyl”), etc. The one or more carbon-carbon doublebonds can be internal (such as in 2-butenyl) or terminal (such as in1-butenyl). Examples of such alkenyl groups include ethenyl (C2),1-propenyl (C3), 2-propenyl (C3), 1-butenyl (C4), 2-butenyl (C4),butadienyl (C4), 1-pentenyl (C5), 2-pentenyl (C5), and the like.

As used herein, “alkynyl” or “alkyne” refers to a radical of astraight-chain or branched hydrocarbon group having from 2 to 4 carbonatoms and one or more carbon-carbon triple bonds (“C2-10 alkynyl”). Insome embodiments, an alkynyl group has 2 to 3 carbon atoms (“C2-3alkynyl”). In some embodiments, an alkynyl group has 2 carbon atoms (“C2alkynyl”). The one or more carbon-carbon triple bonds can be internal(such as in 2-butynyl) or terminal (such as in 1-butynyl). Examples ofC2-4 alkynyl groups include, without limitation, ethynyl (C2),1-propynyl (C3), 2-propynyl (C3), 1-butynyl (C4), 2-butynyl (C4), andthe like.

Alkyl, alkenyl, alkynyl, and aryl groups, as defined herein, aresubstituted or non-substituted, also referred to herein as “optionallysubstituted”. In general, the term “substituted”, whether preceded bythe term “optionally” or not, means that at least one hydrogen presenton a group (e.g., a carbon or nitrogen atom) is replaced with apermissible substituent, e.g., a substituent which upon substitutionresults in a stable compound, e.g., a compound which does notspontaneously undergo transformation such as by rearrangement,cyclization, elimination, or other reaction. Unless otherwise indicated,a “substituted” group has a substituent at one or more substitutablepositions of the group, and when more than one position in any givenstructure is substituted, the substituent is either the same ordifferent at each position. The term “substituted” is contemplated toinclude substitution with all permissible substituents of organiccompounds, any of the substituents described herein that result in theformation of a stable compound. The present disclosure contemplates anyand all such combinations in order to arrive at a stable compound. Forpurposes of this disclosure, heteroatoms such as nitrogen may havehydrogen substituents and/or any suitable substituent as describedherein which satisfy the valencies of the heteroatoms and results in theformation of a stable moiety.

The disclosure also provides synthetic schemes for the inventivecompounds. FIGS. 2 and 11 illustrates an exemplary synthesis forexemplary germole compounds. FIG. 11 also lists the possiblesubstituting aryl (Ar) groups, which may be potential R groups for allgroups of inventive compounds of the present disclosure.

Symmetrical 1,1-disubstituted Germoles

The present disclosure is further directed to the synthesis andcharacterization of these germoles and their AIE effects andapplications. The germoles intensely fluoresce in the blue-green region(478-488 nm) in the solid phase. The electronegativity of the1,1-substituents exhibit a modest inductive effect on the UV-vis andfluorescence wavelength maxima. Although the germoles of the presentdisclosure exhibited higher quantum yields in solution than othercharacterized germoles, their room temperature solutions are only weaklyemissive. In comparison to siloles, the germoles of the presentdisclosure are ca. 3× more emissive in solution, resulting in a smallerenhancement of luminescence when aggregated. The smaller enhancementbetween the luminescence of the molecularly dissolved and aggregatedsolutions of the inventive germoles should not discourage exploiting theAIE effect in these systems. The AIE effect in the germoles of thepresent disclosure is quite pronounced and may be employed in manypotential applications as efficient emitters in aqueous media, coatingmaterials on TLC for chemical or biological sensing, and emissive and/orelectron-transport layer components in organic light emitting diodedevices (OLEDs).

Thus, in one embodiment, the disclosure is directed to a TLC plate fordetection of organic vapor compounds comprising a coating layercomprising a compound having the formula (I)

wherein R₁ and R₂ may be independently selected from optionallysubstituted aryl, optionally substituted heteroaryl, or optionallysubstituted alkynyl. According to one embodiment of the disclosure, R₁and R₂ may be selected independently from the group consisting of

wherein X═H, CF₃, OCF₃,

CH₃, OCH₃, Ph, OPh

and derivatives thereof.

In the TLC plate embodiments, R₁ and R₂ may each be

Referring to FIG. 2, which illustrates an exemplary synthetic scheme forthe symmetrical 1,1-disubstituted germoles of the present disclosure,1,1-Dichloro-2,3,4,5-tetraphenylgermole 1 may be prepared by aring-closure reaction of 1,4-dilithio-1,2,3,4-tetraphenyl-1,3-butadienewith germanium tetrachloride according to the procedure reported byCurtis et al., Am. Chem. Soc. 1969, 91, 6011-6018, which is herebyincorporated by reference to the extent it is consistent herewith. Incontrast to the synthesis of 1,1-dichloro-2,3,4,5-tetraphenylsilole, thegermole 1 can be prepared without difficulty in high yield (70-95%). Thegermole 1 is virtually insoluble in Et₂O and precipitates in relativelyhigh purity from the reaction mixture whereas the related silolerequires a low temperature reaction for the addition step of SiC₁₄.Isolated 1 can be converted to new 1,1-disubstituted germoles (2 through12) by addition of various alkynyllithium reagents that are generatedfrom commercially available terminal acetylenes and ^(n)BuLi. Due to therelatively short lifetime of the lithiated alkyne species, the yields ofgermoles 2 through 12 are lower and varied from 44-70%. Thediphenylphosphine-substituted precursor is not commercially availableand may be prepared according to a known procedure, such as disclosed inHuc et al., Synthesis 2000, 726-730, which is hereby incorporated byreference to the extent it is consistent herewith.

All of these germoles exhibit the unusual phenomenon ofAggregation-Induced Emission (AIE) in the solid state. Germoles 2, 8,and 1,1-diethynyl were tested as potential chemosensors for thedetection of volatile organic compounds (VOCs) such as acetone. Thinfilms of the germoles on TLC silica gel plates showed strong emissionbut upon exposure to acetone the emission is rapidly quenched but afterevaporation of the solvent strong emission resumes.

The germoles of the present disclosure have been characterized bymultinuclear NMR spectroscopy, elemental analyses, X-ray crystallographyand UV-Vis and Fluorescence spectroscopy. Table 1 contains thecrystallographic data for 8 and 12. NMR resonances and couplingsexhibited by germoles 2-12 are within expected values. Table 1 containsthe crystallographic data for 8 and 12.

TABLE 1 Crystallographic Data and Structure Refinement for Compounds 8and 12 8 12 Formula C₄₄H₂₈F₂Ge C₅₆H₄₀GeP₂ Fw 667.29 847.41 cryst size/mm0.32 × 0.33 × 0.38 0.40 × 0.60 × 0.80 cryst syst Triclinic Triclinicspace group P 

P 

a/Å 10.555(2) 11.4828(14) b/Å 11.095(2) 12.9012(13) c/Å 15.680(3)18.022(2) α/deg  92.23(3) 71.258(3) β/deg 104.77(3) 77.857(4) γ/deg113.52(3) 64.911(4) V/Å³ 1607.5(8) 2281.2(4) D_(calcd)/g cm⁻³ 1.3791.234 Z 2 2 abs coeff/mm⁻¹ 0.996 0.778 θ range/deg 1.36 to 34.02 1.20 to24.99 reflns collected/indepreflns 50264/12224 22480/7943 [R(int) =0.027] [R(int) = 0.041] abs correct numerical numerical max. and min.transm 0.7467 and 0.6576 1.000 and 0.8625 final R indices [I > 2σ(I)]0.0395 0.0390 R indices (all data) 0.1121 0.1310

The molecular structures of compounds 2-12 were confirmed by X-raycrystallography. The molecular structures of compounds 8 and 12,respectively, which are exemplary germoles of the present disclosure,are illustrated in FIGS. 3A and 3B. FIGS. 3A and B illustrate the highlytwisted conformation that the phenyl substituents assume relative to thegermacyclopentadiene core. The peripheral phenyl substituents on thering carbons are twisted out of plane with respect to the ring core andare twisted with the same sense within the compound. The averageddihedral angle for the phenyl substituents on the 2,5-ring carbons for2, 4-5, and 7-12 is ca. 38° and for the 3,4-ring carbons ca. 63°. Thedihedral angles reported for 1,1-diphenyl-2,3,4,5-tetraphenylgermole forthe 2,5-ring carbon substituents were 0.7° and 46.1°, while the 3,4-ringcarbon substituents were 96.8° and 63.4°, respectively.

An analysis of the data obtained from the crystal structures suggeststhat the dihedral angles of 2, 4-5, and 7-12 are more similar to thosein tetraphenyl-substituted siloles than the other germole derivativescharacterized by Mullin et al., Inorg. & Organomet. Poly. Mater. 2007,17, 201-203; Tracy et al., Chem. 2005, 44, 2003-2011. As a result ofthese similarities, modifications at the 2,5- and 3,4-positions of thesegermoles may be related to similar effects on the electronic and opticalproperties that have been observed in siloles.

TABLE 2 Selected Torsion Angles (Degrees) of compounds 8, 9, and 11Phenyl substituent attached to ring carbon 8 9 11 C1 Ge1—C14—C15—C16Ge1—C2—C24—C25 Ge1—C31—C17—C35 31.3(3) 33.4(2) −27.3(1) C2C14—C13—C21—C22 C2—C3—C18—C19 C31—C11—C42—C15 63.4(3) 59.1(2) −59.1(1)C3 C13—C12—C27—C28 C3—C4—C12—C17 C11—C30—C19—C37 68.8(3) 65.4(2)−65.9(1) C4 Ge1—C11—C33—C38 Ge1—C5—C6—C11 Ge1—C21—C3—C39 36.3(3) 42.7(2)−46.6(1)

Selected bond lengths and angles illustrate the general agreement of thegeometric parameters for 2, 4-5, and 7-12. The average bond length is1.938 Å for the germoles reported herein. The average C═C and C—C bondlengths of the central ring for 2, 4-5, and 7-12 are 1.357 Å and 1.511Å, respectively The average Si—C bond length was reported to be 1.869 Åwhile the average C═C and C—C bond lengths were 1.363 Å and 1.494 Å,respectively. The exocyclic Ge—C bond lengths are 1.895 Å and 1.893 Å.The C2-Ge—C5 bond angle of the central ring for 2, 4-5, and 7-12 is91.5°.

The absorption spectra for 0.01 mM solutions of germoles 2-12 inmethylene chloride were measured. All of the germoles 2-12 exhibit anabsorption maximum between 364-369 nm. Germoles 2-12 weakly emit in theregion of 478-488 nm in solution at room temperature with quantum yieldsthat range from 0.0046-0.0071 (λ_(ex)=370). Under similar experimentalconditions, germoles 2-12 exhibited quantum yields ca. 3× greater thaneither 1,1-dimethyl- or 1,1-diphenyl-2,3,4,5-tetraphenylgermole forwhich the reported quantum yields were 0.0015 and 0.0026, respectively.

TABLE 3 Absorption and Emission Data for 0.01 mM CH₂Cl₂ Solutions of2-12 at Room Temperature (λex = 370) Absorption Emission Germole λ (nm)λ (nm) Φ_(F)* 4 364 480 0.00457 3 365 478 0.00570 5 365 482 0.00464 9366 485 0.00578 7 366 486 0.00508 6 367 485 0.00569 10 368 487 0.00627 2369 483 0.00582 8 369 488 0.00538 12 369 487 0.00706 11 369 486 0.00689

Consistent with the trend observed for siloles, manipulations of the1,1-substituents imposed a similar shift to longer absorption maxima asthe substituents directly attached to the germanium center increased inelectronegativity. Among a series of germoles possessing the same1,1-substituents, the UV absorption maxima red shifts in the order of Me(350 nm)<Ph (358 nm)<C≡CH (362 nm)<C≡C—R (364-369 nm for 2-12).

Referring to FIG. 4, which is the graph of the absorption spectra forthe methylene chloride solutions of germoles 2 and 4, substitutions onthe β-position of the triple bond (the terminal position of the alkyne)reflect a modest red shift as more electronegative groups areintroduced. This is in contrast to silole derivatives possessing alkynylsubstituents at the 1,1-positions where the absorption and emissionwavelengths remained unchanged despite varying the β-substituents of thealkyne from hydrogens to phenyls. Such data suggests a greatersensitivity in germoles to the identity of the substituents, even thosethat are at more remote bonds from the germanium center and may allowmore control in fine-tuning the electronic properties.

The solid-state photoluminescence is measured using a thin layerchromatography (TLC) method developed by Chen et al, Chem. Mater. 2003,15, 1535-1546, incorporated by reference to the extent it is consistentherewith, and the emission wavelengths are summarized in Table 4. Thethin layer of all the germoles absorbed on the TLC plate fluoresceintensely in the blue-green region. The intensity of the PL emissionsignificantly increased compared to the corresponding weakly emissivesolutions. The trend in the red shift in the emission wavelengths wasnot readily apparent. The germoles of the present disclosure exhibitedStokes shifts between 117-132 nm. These values are consistent with thereported Stokes shift for siloles which vary between 120-129 nm, as wellas those reported for 1,1-dimethyl- or1,1-diphenyl-2,3,4,5-tetraphenylgermole, 117 nm and 130 nm,respectively. Stokes shifts greater than 100 nm are necessary forapplications that require ultra-high sensitivity such as fluorescenceimaging measurements and bioprobes for protein detection andquantification.

TABLE 4 Solid-State Emission Data for 2-12 at Room Temperature (λex =370) Germole Emission λ (nm) Stoke's Shift (nm) 6 484 117 3, 4, 7, 9 485120, 121, 119, 119 2 486 117 11  490 121 5 492 127 8, 12 493 124 10  500132

The present disclosure is also directed to the AIE effect of thegermoles. Referring to FIGS. 5A and 5B, which illustrate the AIE effectin germole 2 at various quantities acetone/water mixtures. Germole 2,which is soluble in acetone as verified by dynamic light scatteringmeasurements but is insoluble in water, is first dissolved in pureacetone and then a specified amount of water is added. Once the water isadded to the mixture, the solubility of 2 is reduced causing aggregationwhich results in an increase in the photoluminescence. As illustrated byFIGS. 5A and 5B, the dilute acetone solution of 2 is weakly emissive;however, as the proportion of water to acetone increased in the mixedsolvent system, the photoluminescence significantly increased. A similarincrease in photoluminescence upon addition of water to either anacetone or acetonitrile solution of the germole has also been observedfor 6, 8, 11, and 1,1-diethynyl-2,3,4,5-tetraphenylgermole. Allvariations within the mixed solvent system exhibited similar spectralprofiles with minimal shifting of the emission wavelength maximum, whichis consistent with similar siloles and germoles. Typically, aggregationresults in a red shift of the emission wavelength. Noteworthy is theindication that the onset of AIE begins at ca. 30% water content withinthe mixed solvent system although the phenomenon is modest. Knownstudies examined similar concentrations of 1,1-dimethyl- and1,1-diphenyl-2,3,4,5-tetraphenylgermole in a variety of mixedsolvent-water systems and reported the earliest occurrence of AIE wasbetween 60-70% water content in a mixed water-dioxane system (Mullin etal., Inorg. & Organomet. Poly. Mater. 2007, 17, 201-213).

FIG. 6 correlates the increase in the PL intensity of 2 with an increasein the emission quantum yield. In FIG. 6, the quantum yields in theacetone and acetone-water mixtures are calculated using9,10-diphenylanthracene as a standard. The quantum yield of the acetonesolution of 2 is 0.0040. A modest increase in the quantum yield to0.0050 is observed at a water content of ca. 30% implying thatintramolecular motions of 2 are already being minimized. Restriction ofthe intramolecular motions of 2 results in increased PL intensity (theAIE effect), which although not discernible by the naked eye, isdetectable with instrumentation. The increased PL intensity is supportedby the increase in quantum yield. When the water content of theacetone-water system is 90%, the quantum yield increases to 0.26, whichis 65 times higher than the acetone solution.

Referring to FIG. 7, which includes the absorption spectra of 0.01 mM 2in the mixed acetone-water solvent systems, all variations within themixed acetone-water solvent system exhibited a similar absorptionspectral profile with broad absorption bands that trail into the longwavelength region and a slight red shift of the wavelength maximum. Thespectral profiles imply that 2 has aggregated in the acetone-watermixtures as both broad absorption bands and red shifts arecharacteristic optical responses related to the Mie scattering effectassociated with the presence of small, metallic particles. Dynamic lightscattering measurements taken within ca. 40 minutes of preparing thesamples also suggest that 2 had aggregated into nanoparticles withaverage sizes of 47 and 74 nm in the acetone-water mixtures with watercontents of 80% and 90%, respectively.

Refer to FIGS. 8A to 8C, which include TEM images of 2 as small andlarge aggregate clusters in water-acetone mixture, to investigate thenature of the aggregate formation in the acetone-water mixtures. In the10% acetone-90% water mixture, the TEM images of 2 depicted theformation of nanoparticles with individual dimensions that are closer to100 nm that aggregate in small clusters (FIG. 8A). The smaller aggregateclusters are more prevalent than the larger aggregate clusters; anexample of one of the larger aggregate clusters is given in FIG. 8B.

The crystalline nature of the particles is confirmed by electrondiffraction patterns (FIG. 8C). As in solid phase crystals, it isreasonable to conclude that the aggregates pack in an arrangement whichminimizes π-π stacking of any planar segments of the germole. Lack ofintermolecular π-π interactions as well as an increased restriction ofany molecular motions imposed by the crystalline lattice would promotethe photoluminescence observed in the acetone-water mixtures.

The present disclosure is further directed to the use of the germoles aschemosensors for the detection of volatile organic compounds.Specifically, the germoles, 2, 8, and1,1-diethynyl-2,3,4,5-tetraphenylgermole were tested as potentialchemosensors for the detection of volatile organic compounds (VOCs) suchas acetone. The photoluminescence was monitored as thin films of thegermoles that were exposed to acetone vapor.

Referring to FIGS. 9A to 9C, which are photos of TLC plates with germole8 before and after exposure to acetone, TLC plates were spotted with˜10⁻³ M methylene chloride solutions of the germoles and allowed tothoroughly dry in air. As can be seen in FIG. 9A, the thin film of 8intensely fluoresces. Upon exposure to acetone vapor, the emission israpidly quenched (FIG. 9B). This is consistent with the acetone vaporcondensing on the TLC plate and dissolving the germole which quencheslight emission, representing the “OFF” switch. Once the acetone vaporevaporates, the emission resumes (FIG. 9C) suggesting that the germoleaggregates and once again, emits light, representing the “ON” switch.This luminescence switch behavior has been observed for all three of thegermoles tested and can be repeated multiple times without diminishingthe light emission.

The solid state photoluminescence of AIE(E) molecules can be furtherenhanced by crystallization which commonly occurs during the annealingprocess of thin films in OLEDs and is detrimental to the luminescence ofconventional luminophors (ACQ effect). According to thecrystallization-enhanced emission (CEE) theory, the intramolecularrotations of the peripheral aryl substituents are even more restrictedwithin a crystal lattice as compared to an amorphous solid which canenhance light emission by several orders of magnitude. The RIR mechanismgives rise to the AIE(E) phenomenon which has been observed in Group 14metalloles containing aryl substituents. The strong emission in both thecrystalline and amorphous solid states exhibited by Group 14 metallolesmakes them ideal candidates for a variety of applications such as activelayers for EL devices and as chemical and biological sensors.

In the packing arrangement of hexaphenylsilole (HPS) and1,1-diethynyl-2,3,4,5-tetraphenylsilole, multiple CH-π bonds wereidentified that were propose to further aid in restrictingintramolecular motions of the aryl substituents by locking theconformation within the crystalline lattice which enhanced the PLemission (Dong et al., Inorg. Organomet. Polym. 2007, 17, 673-678).

Referring to FIGS. 10A and 10B, which closely examine the packingarrangement of the crystals of 8 for evidence of any cooperative bondinginteractions, the crystal structure of 8 illustrates that adjacentmolecules pack in such a way that the phenyl substituents arepractically orthogonal and cannot overlap. The closest distance betweenthe 3,4-phenyl substituents of two adjacent molecules of 8 is 6.9 Å(FIG. 10A), which is too great a distance for any π-π stacking or CH-πinteractions. The ring cores are staggered with respect to one anotherwith an interplane distance between the germole cores of 10.5 Å (FIG.10B), too great a distance for any intermolecular interactions. Thereare, however, multiple CH groups as well as fluorine atoms present in 8that may participate in non-conventional, weak CH-π hydrogen bonding intwo regions within the packing arrangement. Both potential cooperativeinteractions involve the substituted phenyl ring of one of the1,1-substituents with the phenyl substituents on an α-carbon in the ringcore and another 1,1-substituent of a second molecule located directlyabove (FIG. 10B). The distances between these segments are 3.0 Å and 2.7Å, respectively. These measurements are within hydrogen-bonded andintermediate (type CH—X) intermolecular approaches of ca. 3.0 Å whichwere demonstrated for edge-to-face orientations in several siloles.Hence crystallization of 8 does not diminish photoluminescence. All thesymmetric 1,1-disubstituted germoles exhibit strong solid luminescencein both the amorphous and crystalline phases.

Research Summary for Unsymmetrical 1,1′-disubstituted Germoles,Germafluorenes, Germa-rhodamines/Germa-fluoresceins and Germapins

Research strategies for designing luminescent Group 14 moleculesdescribe the preparation of a) unsymmetrical 1,1′-disubstituted germolesand b) functionalized germafluorenes,germa-fluoresceins/germa-rhodamines, and germapins. These syntheticpathways build on a variety of established reactions and allowincorporation of structural features that promote aggregation-inducedemission (AIE(E)). Mechanistic studies of molecules that exhibit theAIE(E) effect indicate that their unique propeller-like structures arevital to photoluminescence in the solid state. These molecules possessmultiple peripheral aryl substituents that function as “blades” thatrotate around single or double bond axles that link them to a centralconjugated core. Steric congestion restricts the intramolecularrotations (RIR) of the peripheral aryl substituents causing the groupsto twist relative to the core. Hence, the propeller-like shape preventsπ-π stacking interactions with neighboring fluorophores in condensedphases such as aggregates or the solid state minimizing excimerformation and resulting in strong light emission.

These luminophors possess exceptional optoelectronic properties and areexcellent candidates for solid state applications as components inOLEDs, (OFETs), host materials, and solar cells. Major emphasis is beingplaced on the development of air stable blue and the more rare redlight-emitting molecules with high electron affinities and mobilitiesthat meet specifications for organic semiconducting materials.

The present disclosure is directed to a series of1-phenyl-1′-substituted germoles, where the 1′-substituent can be avariety of (aryl)ethynyl groups bound to the Ge center. Groups wereselected for their ability to enhance emission in the solid statethrough AIE(E). The present disclosure is also directed to the synthesisof germafluorenes, germanium-based fluoresceins/rhodamines, andgermapins. Synthetic methods were used to allow for structuralmodification of the organic framework, the central ring and thegermanium center of these larger heterocycles to target both blue andred-emitting molecules for solid state applications. Many of theoptoelectronic properties of these molecules are intricately tied totheir electronic structures which can be tuned by incorporating avariety of functional groups, fusing aromatic rings, or introduction ofheteroatoms.

Unsymmetrical 1,1′-disubstituted Germoles

One aspect of the present disclosure involves the synthesis of newunsymmetrical, 1,1′-disubstituted-2,3,4,5-tetraphenyl- and2,3,4,5-tetra(aryl)germoles to examine both the steric and electroniceffects of the substituents on the ring and at the Ge center on thesolid state luminescent properties and efficiencies. Unsymmetrical1,1′-germoles exhibit significantly higher quantum efficiencies in thesolid state than their symmetrical congeners. Related siloles differingin 1,1′-substitution exhibited higher solid state quantum efficienciescompared to the symmetrical 1,1-substituted siloles due to the higherdifficulty in packing compactly in the solid state. In addition, the useof phenyl substituents on the germanium center lowers the LUMO energylevel, an effect that has been observed with siloles which has beenattributed to extended σ*-π* conjugation between the silicon center andthe phenyl ring.

1-chloro-1-phenyl-2,3,4,5-tetraphenylgermole 42 (FIG. 11, Scheme 4) canbe produced by addition of commercially available PhGeCl₃ in a reactionanalogous to that used to produce germole 29.

Other diarylacetylenes (PhC≡CPh, PhC≡CSiPr₃ and ArC≡CPh(Ar=2,6-diisopropylphenyl)) can be reacted with lithium metal in asimilar fashion as described for 1 for the construction of new1,1′-disubstituted-2,3,4,5-tetra(aryl) germoles. A palladium-catalyzedone-pot synthesis of symmetric diarylacetylenes is utilized to prepareprecursors analogous to germole 1.1-chloro-1-phenyl-2,3,4,5-tetra(aryl)germoles utilizing the symmetricaldiarylacetylenes, ArC≡CAr (Ar=p-tolyl, biphenyl, and p-methoxyphenyl) isprepared. Scheme 4 shows the synthetic routes that produce a series ofnew 1,1′-unsymmetrically substituted germoles beginning with germole 13.Related 1-aryl-1-chloro-2,3,4,5-tetraphenylgermoles were prepared bydirect reaction of 1 with an aryl-Grignard reagent, ArMgX(Ar=p-(NMe₂)C₆H₄, p-MeC₆H₄, C₆F₅). This aspect of the present disclosurebuilds functionality at the 1-germole position via the Ge—Cl unit.Reaction of germole 13 with arylalkynyllithium reagents would producenew germoles 15a-o. Alternatively, palladium-catalyzed couplingreactions can be performed to introduce an array of different arylgroups by reaction of the 1-ethynyl group in 14 with an aryl iodide orbromide if the desired substituted terminal alkynes are not commerciallyavailable. Germole 14 has not been reported in the literature, but thecorresponding silole has been prepared by the analogous reaction shownin Scheme 4.

The use of the ethynyl group bound directly to the germole core isdesirable as it extends the conjugation of the metallole ring andenables incorporation of a variety of aryl substituents that would betoo sterically demanding if bound directly to the germanium center. TheSonogashira-type coupling described in Scheme 4 is tolerant of a varietyof functional groups. The synthesis of related unsymmetrical1,1′-disubstituted siloles have been reported utilizing Sonogashiracoupling reactions but the preparation of unsymmetrical1,1′-disubstituted germoles is limited. Related oligomers from1,1-diethynyl-2,3,4,5-tetraphenylsilole and aryl and heteroaryl bromidesand iodides have been prepared in the presence of a Pd catalyst. In oneaspect of the present disclosure, ethynyl-substituted aromatics andthiophenes which are suitable for the synthetic route shown in Scheme 4were prepared (See FIG. 11).

With the aim of developing high efficiency solid state luminescence inGroup 14 heterocycles, structural modifications were explored thatpromote the AIE(E) processes. Many of the structural prerequisites thatpromote these two processes can be readily incorporated into Group 14containing heterocycles to minimize the problems that are oftenassociated with luminogens that quench upon aggregation thus renderingthem ineffective for solid state applications. By studying thestructure-property relationship of Group 14 heterocycles, an array ofhighly luminescent molecules that span a wide range of the visiblespectrum including the blue and more rare red-emitting regions wereprepared. Based on the AIE(E) processes, new germanium heterocycles suchas germafluorenes, germanium-based fluorescein/rhodamine analogs, andgermapins which all possess structural similarities to known AIE(E)luminophores were prepared. Synthetic procedures are described belowthat allow for covalent decoration of germanium heterocycles that alsoinclude examples with heteroatom substituents. Although processes suchas donor-acceptor push-pull interactions, J-aggregate formation, ortwisted intramolecular charge transfer (TICT) between polar functionalgroups do not activate the AIE(E) effect, incorporation of these groupsinto the heterocycles allows for control of the emission color providingluminophors that cover the entire visible spectrum.

Germafluorenes

In order for materials to find practical applications aselectron-transporting or emissive layers as thin films in semiconductingand electronic devices, a luminophor should exhibit two majorcharacteristics: fast electron injection/transport abilities and highfluorescence quantum yield (Φ_(F)) in the solid state. Few organicmolecules can exhibit both air stability and high electron mobility.Additionally, many organic fluorophores experience quenching uponaggregation (ACQ effect) thus rendering them ineffective for solid stateapplications. The Group 14 heterocycles provide a unique solution tothese problems. Studies have established the superior solid stateproperties of Group 14-based luminogenic molecules and materials,particularly those of germafluorene, for electroluminescent applicationscompared to their carbon analogs. These air stable Group 14 heterocyclespossess extremely low LUMO energies necessary for fast electroninjection/transport abilities and high thermal stabilities while theiraggregation-induced emission (AIE) properties allows for the developmentof luminophors whose aggregates fluoresce more strongly than theirsolutions. The Group 14 molecules described herein exhibit interestingand highly promising optoelectronic and chemical properties that enablethem to participate in a number of electroluminescent device andchemosensor applications that will benefit technological advancementsand safety benefits for society.

These superior optoelectronic properties have also been observed inrelated, but larger ring systems such as 9-sila- or 9-germafluorenes,respectively, which have become prominent building blocks inpolymer-based materials. Efforts to improve upon these materials haveprovided insight into the potential of germanium-containing analogswhich have been studied to a lesser extent despite exhibiting propertiessimilar to silicon. This germanium heterocycle is an excellent bluelight-emitting and host material. Germafluorenes have demonstratedsignificantly higher maximum luminescence efficiencies in the samepolymer light-emitting diode (PLED) device configurations as that ofsilafluorene and the electrochemical redox behavior supports thepresence of an even lower lying LUMO than that of silicon. This datasupports the better electron injection and transfer abilities ofgermafluorene than that of its silicon analog.

The greater impact of germanium over silicon has also been demonstratedby higher power conversion efficiencies (PCE) when germafluorenecopolymers were used as the active light absorbing layer or p-typematerial in inverted bulk heterojunction (BHJ) solar cells. In thesesystems, the redox behavior of germafluorene copolymer indicated ahigher HOMO energy level than that of silafluorene under identicalconditions translating into a larger energy gap between the HOMO (p-typematerial) and LUMO (n-type material) which is vital for thedetermination of the open circuit voltage of the solar cell. Similarresults were obtained with Group 14 metalloles where calculated valuesfor germole-containing oligomers indicated higher HOMO energy levelsthan those of siloles. As such, the synthesis andphoto/electroluminescence properties of germanium heterocycles as activecomponents in optical and electronic devices are beneficial.

In one embodiment of the present disclosure, the compounds are a seriesof substituted germafluorenes having the general formula (II)

wherein R₁ and R₂ may be independently selected from the groupconsisting of aryl, alkyl, halide, alkynyl, and asymmetric derivativesthereof with two different groups at the Ge-center; wherein R₃ and R₆may be independently selected from the group consisting of Y and

wherein R₄ and R₅ may be independently selected from the groupconsisting of OCH₃ and Y; andwherein Y is H,

wherein Z is F, CH₃, or OCH₃;

wherein X is H, CF₃, OPh, CH₃, Ph, OCH₃ or OCF₃; or

wherein R is aryl, alkenyl or alkynyl.

FIG. 12 illustrates an exemplary synthesis for germafluorenes, withadditional substituting Ar groups. FIG. 15 depicts the crystal structureof one exemplary germafluorene.

Sila- and germafluorenes are of particular interest to this disclosuresince they are increasingly being used as key building blocks inconjugated copolymer systems. The related polyfluorenes which have beenused to construct high performance polymers suffer from a majordisadvantage in that they are prone to oxidation at the C-9 carbonposition upon heating resulting in a red shift in the emission, reducedemission efficiency and color degradation. Significant improvements inemission efficiency, enhanced electron injection and transport abilitiesas well as stable blue emission have been achieved by incorporatingsila-, and germafluorene in place of fluorene in (co)polymers. Inaddition to these exceptional properties, thermogravimetric analysis(TGA) evaluation of germafluorene copolymers indicate good thermalstabilities that exceed 400° C.

Efforts by researchers have shifted to the development of singlemolecule germafluorenes for applications in organic electronic devicesand thus a series of 2,7-disubstituted-3,6-dimethoxygermafluorenes wassynthesized using a modified procedure reported by Huang for thepreparation of 6,6′-dilithio-4,4′-dibromo-3,3′dimethoxybiphenyl from thecorresponding 6,6-diodo-biphenyl precursor. Subsequent reaction withPh₂GeCl₂ provided the target 2,7-dibromo-3,6-dimethoxygermafluorene.Germafluorene 16 was reacted with two different aryl-substituted alkynes(HCCAr) under standard Sonagashira cross-coupling conditions to affordtwo new 2,7-disubstituted(alkynyl)-3,6-dimethoxygermafluorenes 17 and 18(FIG. 12). Other related silafluorene analogs have been prepared by asimilar synthetic route.

Investigations of germafluorenes 17 and 18 suggest that these compoundsare AIEE molecules as they exhibit intense blue emission in solution(λabs˜375 nm, λem=426 nm) (FIGS. 13A-13D) as well as in the solid state(FIGS. 14A-14C). The germafluorenes are soluble in a wide range ofcommon organic solvents which allow uniform thin films to be drop castfrom standard solutions for future cyclic voltammetry and devicefabrication studies. In the solid phase, the emission was measured atca. 430 nm using a thin layer chromatography (TLC) technique.Determination of the fluorescence quantum yields in solution usinganthracene in ethanol as a standard was undertaken. Germafluorene 17exhibited a quantum yield of 0.77. Related silicon derivatives exhibit aslightly lower Φ_(F) value under similar conditions. Remarkably, thesenew 2,7-disubstituted germafluorenes demonstrated exceptional stabilityin air and solution. The absorption and emission maxima and intensitywere unchanged for solutions stored in standard vials under ambientconditions after 2 years in CH₃CN or acetone (FIGS. 13A-13D). Uponvisual inspection, the luminescence intensity of the germafluorenes,even at more dilute concentrations, resembles a solution9,10-diphenylanthracene, a common standard used for determination offluorescence quantum yields. Germafluorene 17 demonstrated a hightolerance to photobleaching under high energy (254 nm) for prolongedperiods of time.

The molecular structures for the two new germafluorenes 17-18 wereconfirmed by X-ray crystallography. FIG. 15 displays the molecularstructure of 17 that exhibits an almost planar germanium containingcentral core which promotes efficient σ*-π* conjugation and as a resultthe alkynyl linker at the 2,7-positions can assume a flexibleorientation. A significant separation is observed in the packingstructure between molecules thus preventing intermolecular electronicinteractions such as π-π stacking that would lead to luminescencequenching. The central core of the germafluorene ring system providesthree sites for the study of structure-property relationships. In oneaspect of the present disclosure, the use of phenyl substituents boundto the Ge center is disclosed since they provide steric congestionrequired to disturb packing arrangements that promote AIE(E) propertiesand enhance the thermal stability of the molecules. However, a varietyof groups can be utilized to promote these properties includingsubstituted aryl groups (i.e. p-tolyl), and linear hydrocarbon groupssuch as n-butyl. Functionalization at the para-positions can be achievedby replacement of the methoxy groups with phenyl, p-tolyl, or mesitylsubstituents utilizing a Ni-catalyzed cross-coupling reaction involvingthe corresponding aryl Grignard reagent (FIG. 12, 19). This method hasbeen successful for the modification of a 3,6-dimethoxysilafluorene withPhMgBr. The research involved the synthesis of an array of newgermafluorenes by the reaction sequence presented in FIG. 12 utilizing arange of alkynyl-based substituents to introduce functional groups atthe 2,7-positions for the preparation of 19 c-g. The alkynyl-basedreagents that were investigated are either commercially available orreadily prepared by literature procedures from the correspondingbromide.

Germa-Rhodamines/Germa-Fluoresceins

In another embodiment of the present disclosure, the compounds aresubstituted germa-fluoresceins or germa-rhodamines having the generalformula (III)

wherein R₁ and R₂ may be independently selected from the groupconsisting of aryl, alkyl, halide, alkynyl, and asymmetric derivativesthereof with two different groups at the Ge-center; wherein R₄ and R₇may be independently selected from the group consisting of ═O, —OH, andOSi(CH₃)₂[C(CH₃)₃] hydroxyl or carbonyl amine and ether derivatives;wherein R₅ and R₆ are H; and,wherein R₃ is Y, ═O, C₆H₅, p-CH₃C₆H₅, p-CH₃OC₆H₅ or

wherein Y is

wherein Z is F, CH₃ or OCH₃;

wherein X═CF₃, OPh, CH₃, Ph, OCH₃ or OCF₃;

wherein NR₂═NH₂, NMe₂ or NEt₂ and Z=Me, CO₂H, C(═O)H, or CO₂Me;

wherein R is alkyl and Z=Me, CO₂H, C(═O)H, or CO₂Me; or,

wherein R is alkyl or H.

FIG. 16 illustrates an exemplary synthesis for germa-fluoresceins andgerma-rhodamines. In one aspect of the present diclosure, formula (III)includes germaanthracenes. Germaanthracene analogs are highly conjugatedand have a six-membered planar ring at the core of the molecule.

The anthracene motif has been successfully used as the core of severalwell known and highly fluorescent molecules such as fluorescein andrhodamine which have been invaluable to biological research applicationsas labels and sensors for biomolecules, probes for various biologicallyrelevant metals and enzymatic activities, and in vivo/in vitro cellimaging. These dyes have many photophysical properties, such as highfluorescent intensity and quantum yields, long excitation and emissionwavelengths, and tolerance to photobleaching for the development of redlight-emitting Ge-fluorescein derivatives.

Red OLEDs are a vital component of full color displays; however,red-light emitting materials with high electroluminescence abilities andthermal stabilities are more limited in number than blue and greenlight-emitters. Red-light emitting materials are typically used only asdopants in OLED fabrication which presents multiple problems associatedwith reliably reproducing the concentration of the doped material forcommercial production. Non-doped pure red OLEDS are rare. The difficultywith red light emitting luminophors is that they suffer fromaggregation-caused quenching (ACQ) of light emission as they commonlypossess one of two characteristics: highly conjugated π-systems or polardonor-acceptor substituents. Either characteristic renders theseluminophors prone to crystallization in the solid state which ultimatelyleads to ACQ and the irreversible loss of fluorescence.

Several Group 14 fluorescein and rhodamine derivatives have beenreported whereby the oxygen atom at the ten position of the xanthenemoiety has been replaced with silicon or germanium. Two important factshave emerged from these studies. Introduction of silicon or germanium atthe ten position within these analogs leads to a significant red shiftof the emission and excitation wavelengths which has been attributed tothe low-lying LUMO energy levels associated with Group 14 elements. Theshift to longer wavelengths has enabled the development of severaloutstanding far-red to near infrared fluorescence probes for biologicalimaging while retaining all of the desirable photophysical properties offluorescein and rhodamine. Secondly, the fluorescence mechanism inseveral of the fluorescein analogs can be activated without difficult tocontrol strategies such photoinduced electron transfer (PeT) orspiro-cyclization which are typical in both fluorescein and rhodamine.These studies suggest that is possible to extend the range offluorescein-based molecules without labor-intensive syntheticstrategies. Although no crystal structures of these novel molecules wereprovided in these studies, it is not unreasonable to assume that thearyl substituent located at position 5 of the xanthene moiety is twistedrelative to the xanthene core just as it is in fluorescein. In otherwords, these fluorescein-based molecules already possess the twistedstructure necessary for AIE(E).

In one embodiment of the present disclosure, the compound of formula(III) may have the formula (III-A)

wherein R₁ and R₂ may be independently selected from the groupconsisting of aryl, alkyl, halide, alkynyl, and asymmetric derivativesthereof with two different groups at the Ge-center; wherein R₃ isselected from the group consisting of C₆H₅, p-CH₃C₆H₅, p-CH₃OC₆H₅, andanother substituted aromatic substituent; and, wherein R_(q) is H oranother substituted aromatic substituent.

Germapins

In yet another embodiment of the present disclosure, the compounds aresubstituted germapins having the general formula (IV)

wherein R₁ and R₂ may be independently selected from the groupconsisting of aryl, alkyl, halide, alkynyl, and asymmetric derivativesthereof with two different groups at the Ge-center; wherein R₃ and R₆may be independently selected from the group consisting of H, Cl, Ar, Yand

wherein R₄ and R₅ may be independently selected from the groupconsisting of H, aryl, I, Br, Y or

andwherein Y is

wherein Z is F, CH₃ or OCH₃;

wherein X is CF₃, OPh, CH₃, Ph, OCH₃ or OCF₃; or

wherein R is aryl, alkenyl or alkynyl.

FIG. 17 illustrates an exemplary synthesis for germapins.

The present disclosure is also directed to the changes that occur in theoptical and electrical properties of the molecules disclosed herein asthey are modified in size and shape of the central conjugatedgermanium-containing core. The germapin serves as another uniquescaffold for developing strong blue light emitting AIE(E) molecules.Surprisingly, only two germapins have been reported, 5,5-diphenyl- and5,5-dimethyl-9,10-dihydrido-5H-dibenzo. The crystal structure of thediphenyl derivative exhibited the unique boat conformation that thecentral seven-membered ring assumes. The silicon analogs, silepins, areair and moisture stable solids which exhibit strong blue fluorescence insolution with quantum yields ranging from 0.40 to 0.93 depending on thesite and the type of substitutent incorporated into the conjugatedframework.

The synthesis for the germapins is based on a method used by Clegg andcoworkers for the preparation of functionalized silapins (shown inScheme 6, FIG. 17). The stilbene precursor 27 which is key to thismethod is prepared by a Wittig reaction between a phosphonium aryl saltand a dihalogenated aldehyde in excellent yields and highcis-selectivity. The dichloro-substituted germapin is then obtained by aring closing reaction between the in situ generated dilithiointermediate and an appropriate dichlorogermane. A variety ofsubstituted derivatives are prepared from the dichloro-germapin 28 whichis stable enough to participate in multiple standard cross-couplingreactions such as Suzuki, Stille, and Sonogashira. Initial studies beganwith Ph₂GeCl₂ and simple aryl bromides such as those described for thepreparation of other germanium heterocyles (FIG. 12). The preparation ofunsymmetrical germapins is also accomplished by modifying the stilbeneprecursor which can be done by using a trihalogenated aldehyde in theWittig reaction.

In one embodiment of the present disclosure, the compound of formula IVmay have the formula (IV-A)

wherein R₇ and R₈ may be independently selected from the groupconsisting of aryl, alkyl, halide, alkynyl, and asymmetric derivativesthereof with two different groups at the Ge-center.

In another embodiment of the present disclosure, the compound of formulaIV may also have the formula (IV-B)

wherein R₉ and R₁₀ may be independently selected from the groupconsisting of aryl, alkyl, halide, alkynyl, and asymmetric derivativesthereof with two different groups at the Ge-center.

EXAMPLES

All reactions of Examples 1-13 were performed under an inert atmosphereof argon using flame or oven dried glassware on a dual-manifold Schlenkline or in a drybox. Diethyl ether and THF were distilled oversodium/9-fluorenone prior to use. Methylene chloride was distilled overCaH₂. Chloroform-d was purchased from Cambridge Isotopes Inc., and driedover activated molecular sieves. Other commercially available reagentswere purchased from Aldrich Chemical Co. and were used as received. NMRspectra were recorded on Bruker Avance-300 MHz and Bruker ARX-500 MHzinstruments at ambient temperature. Spectroscopic data were recorded at300 MHz and 500 MHz respectively for ¹H, 125 MHz and 75 MHz respectivelyfor ¹³C, 202 MHz for ³¹P, and 282 MHz for ¹⁹F. Proton, carbon,phosphorus, and fluorine chemical shifts (δ) are reported relative tothe residual protio and deuterio-chloroform, external H₃PO₄ and CFCl₃,respectively. Chemical shifts are reported in ppm and the couplingconstants in hertz. Melting point determinations were obtained on aMel-Temp melting point apparatus and are uncorrected. UV-vis andfluorescence spectra were measured on a Cary 50 Bio UV-visible and CaryEclipse Fluorescence spectrophotometer, respectively. Emission spectrawere measured using the λ_(max) value for each compound as determined bythe absorption spectra. Elemental analysis determinations were performedby Atlantic Microlabs, Inc., Norcross, Ga. The X-ray crystallographicdata were collected on a Bruker Apex II diffractometer equipped with aCCD area detector.

For solid state PL measurements, aluminum TLC plates (Merck, Silica 60F₂₅₄) were used. Dichloromethane solutions of the germoles (0.67 mg/ml)were used as the developing media. The coated TLC plates were excited atan angle of 20° in the spectrofluorometer. For dynamic light scatteringmeasurements, the hydrodynamic radius (RH) was measured at roomtemperature with a DynaPro Titan instrument (Wyatt Technology, SantaBarbara, Calif.). Samples (30 μL) were placed directly into a quartzcuvette, and light scattering intensity was collected at a 90° angleusing a 10 s acquisition time. Data regularization with Dynamics(version 6.7.1) generated histograms of percent mass versus RH.

For TEM images, a droplet of 0.05 mM acetone-water mixture was appliedto a lacey carbon film on a square mesh copper grid (Ted Pella Inc.) andallowed to air dry at 25° C. The aggregated samples were visualized witha Phillips EM 430 transmission electron microscope operated at 300,000eV and magnifications of 110,000 and 150,000, respectively.

For SEM images, thin films were prepared by coating quartz slides withca. 10⁻³M methylene chloride solutions of the germoles. The morphologieswere visualized with a JEOL-6320F Field Emission scanning electronmicroscope (SEM) after sputtering a thin layer of gold onto the sampleswith a Hummer VI sputtering system. The operating parameters for theimages were taken with the lower detector were: an acceleration voltageof 5 keV, probe current #3, objective lens aperture 3, and a workingdistance of 15 mm. The operating parameters for higher detector weresimilar except that an acceleration voltage of 15 keV and a workingdistance of 8 mm were employed.

Example 1 Formation of 1,1%Bis(4-(trifluoromethyl)phenyl)-2,3,4,5-tetraphenylgermole (2)

A solution of n-BuLi (0.50 mL, 2.5 M in hexane, 1.3 mmol) was addeddropwise to a solution of 1-ethynyl-4-trifluorotoluene (0.20 mL, 1.3mmol) in dry THF (1.5 mL) that had been cooled to −78° C. Once theaddition was complete, the colorless reaction mixture was stirred atthis temperature for 15 minutes. The resulting alkynyllithium solutionwas then added in one portion to a solution of1,1′-dichloro-2,3,4,5-tetraphenylgermole (0.31 g, 0.63 mmol) in dry THF(5 mL) that had been cooled to 0° C. The yellow reaction mixture wasallowed to gradually warm to room temperature and stirred overnight. Thereaction mixture was quenched with water (0.25 mL), stirred for anadditional 15 minutes, and then dried over MgSO₄. After filtering, thesolvent was removed by rotary evaporation. The crude product waspurified on a silica gel column using a toluene/hexane (2:1) as theeluent to give 2 as a yellow solid (340 mg, 71%). X-ray quality crystalswere grown by slow evaporation from a methylene chloride/diethyl ethermixed solvent system. All of the other germoles were prepared in asimilar manner. The eluent and recrystallization solvent systems used inthe purification of each germole are indicated.

Example 2 Formation of1,1-Bis(4-(trifluoromethyl)phenyl)-2,3,4,5-tetraphenylgermole (2)

M.p. 179-180° C. ¹H NMR (500 MHz): δ 7.63 (d, J=8 Hz, 4H), 7.57 (d, J=8Hz, 4H), 7.22 (d, J=8 Hz, 4H), 7.16 (t, J=8 Hz, 4H), 7.14-7.09 (m, 2H),7.09-7.03 (m, 6H), 6.91-6.86 (m, 4H). NMR (125 MHz): δ 153.5, 138.4,137.7, 135.4, 132.7, 130.9 (q, J=33 Hz), 129.85, 129.80, 128.2, 127.9,127.0, 126.9, 126.2, 125.3 (q, J=8 Hz), 124.9, 105.8, 88.6. ¹⁹F{¹H} NMR(282 MHz): δ −62.9. Anal. Calcd. for C₄₆H₂₈F₆Ge: C, 72.00; H, 3.68;Found: C, 71.74; H, 3.57.

Example 3 Formation of1,1-Bis(4-(trifluoromethoxy)phenyl)-2,3,4,5-tetraphenylgermole (3)

Purification of (3) by column chromatography using silica gel andtoluene/hexane (2:1) as the eluent yielded a yellow solid (461 mg, 67%).M.p. 113-114° C. ¹H NMR (500 MHz): δ 7.61-7.57 (m, 4H), 7.28-7.25 (m,4H), 7.22-7.17 (m, 8H), 7.17-7.14 (m, J=5, 2 Hz, 2H), 7.13-7.07 (m, 6H),6.94-6.90 (m, 4H). ¹³C{¹H} NMR (125 MHz): δ 153.4, 149.6, 138.6, 137.8,135.8, 134.1, 129.9, 129.8, 128.2, 127.9, 126.9, 126.8, 121.3, 120.9,119.5, 105.8, 86.9. ¹⁹F{¹H} NMR (282 MHz): δ −57.7. Anal. Calcd. ForC₄₆H₂₈F₆GeO₂: C, 69.12; H, 3.53; Found: C, 68.71; H, 3.59.

Example 4 Formation of1,1-Bis(p-tolylethynyl)-2,3,4,5-tetraphenylgermole (4)

Purification of (4) by column chromatography using silica gel andhexane/toluene (2:1) as the eluent yielded a yellow solid (317 mg, 70%).Yellow crystals were grown by slow evaporation from a methylenechloride/hexane mixed solvent system. M.p. 210.5-212° C. NMR (CDCl₃): δ7.45 (d, J=8 Hz, 4H), 7.31-7.27 (m, 5H), 7.20-7.12 (m, 10H), 7.11-7.05(m, 6H), 6.94-6.90 (m, 4H), 2.38 (s, 6H). ¹³C{¹H} NMR (125 MHz): δ152.9, 139.4, 138.8, 138.1, 136.4, 132.4, 130.0, 129.8, 129.1, 128.1,127.8, 126.7, 126.6, 119.6, 107.5, 85.2, 21.7. Anal. Calcd. forC₄₆H₃₄Ge: C, 83.79; H, 5.20; Found: C, 83.46; H, 5.64.

Example 5 Formation of1,1-Bis((4-methoxyphenyl)ethynyl)-2,3,4,5-tetraphenylgermole (5)

Purification of (5) by column chromatography using silica gel andtoluene/hexane (2:1) as the eluent yielded a yellow solid (200 mg, 46%).Yellow crystals were grown by slow evaporation from atetrahydrofuran/methanol mixed solvent system. M.p. 250-252° C. ¹H NMR(500 MHz): δ 7.48-7.43 (m, 4H), 7.24 (m, 4H), 7.14 (m, 4H), 7.11-7.06(m, 2H), 7.06-7.01 (m, 6H), 6.90-6.86 (m, 4H), 6.84-6.80 (m, 4H), 3.79(s, 6H). ¹³C{¹H} NMR (125 MHz): δ 160.3, 152.8, 138.9, 138.2, 136.5,134.0, 129.9, 129.8, 128.1, 127.8, 126.7, 126.5, 114.8, 113.9, 107.3,84.4, 68.1, 55.4, 25.7. Anal. Calcd. for C₄₆H₃₄GeO₂. 1 C₄H₈O: C, 78.65;H, 5.54; Found: C, 78.45; H, 5.42.

Example 6 Formation of1,1-Bis((1,1-biphenyl)-4-ylethynyl)-2,3,4,5-tetraphenylgermole (6)

Purification of (6) by column chromatography using silica gel andhexane/toluene (2:1) as the eluent yielded a yellow solid (282 mg, 58%).Yellow crystals were grown by slow evaporation from atetrahydrofuran/methanol mixed solvent system. M.p. 186-188° C. ¹H NMR(500 MHz): δ 7.63-7.53 (m, 12H), 7.47-7.41 (m, 4H), 7.38-7.34 (m, 2H),7.29-7.27 (m, 4H), 7.19-7.14 (m, 4H), 7.13-7.09 (m, 2H), 7.08-7.03 (m,6H), 6.93-6.87 (m, 4H). ¹³C{¹H} NMR (125 MHz): δ 153.1, 141.9, 140.4,138.8, 138.0, 136.2, 132.9, 129.98, 129.87, 129.0, 128.2, 127.92,127.88, 127.2, 127.0, 126.8, 126.7, 121.5, 107.2, 86.7. Anal. Calcd. forC₅₆H₃₈Ge: C, 85.84; H, 4.89; Found: C, 85.86; H, 4.82.

Example 7 Formation of1,1-Bis((4-phenoxyphenyl)ethynyl)-2,3,4,5-tetraphenylgermole (7)

Purification of (7) by column chromatography using silica gel andhexane/toluene (2:1) as the eluent yielded a yellow solid (254 mg, 50%).Yellow crystals were grown by slow evaporation from atetrahydrofuran/methanol mixed solvent system. M.p. 204-205° C. ¹H NMR(500 MHz): δ 7.54-7.49 (m, 4H), 7.42-7.36 (m, 4H), 7.30-7.25 (m, 4H),7.20-7.15 (m, 6H), 7.14-7.10 (m, 2H), 7.10-7.07 (m, 6H), 7.06-7.02 (m,4H), 6.96-6.92 (m, 4H), 6.92-6.89 (m, 4H). ¹³C{¹H} NMR (125 MHz): δ158.4, 156.4, 153.0, 138.8, 138.1, 136.3, 134.2, 130.1, 130.0, 129.8,128.1, 127.9, 126.8, 126.6, 124.1, 119.7, 118.2, 117.1, 106.9, 85.2.Anal. Calcd. for C₅₆H₃₈GeO₂: C, 82.47; H, 4.70; Found: C, 82.16; H,4.82.

Example 8 Formation of1,1-Bis((3-fluorophenyl)ethynyl)-2,3,4,5-tetraphenylgermole (8)

Purification of (8) by column chromatography using silica gel andhexane/toluene (2:1) as the eluent yielded a yellow solid (271 mg, 65%).Yellow crystals were grown by slow evaporation from a methylenechloride/hexane mixed solvent system. M.p. 181.5-182.5° C. ¹H NMR (500MHz): δ 7.32-7.28 (m, 4H), 7.22 (m, 6H), 7.16 (m, 4H), 7.13-7.09 (m,2H), 7.08-7.03 (m, 8H), 6.90-6.86 (m, 4H). ¹³C{¹H} NMR (125 MHz): δ162.4 (d, J=247 Hz), 153.3, 138.6, 137.8, 135.7, 130.0 (d, J=9 Hz),129.9, 129.8, 128.3 (d, J=3 Hz), 128.2, 127.9, 126.9, 126.8, 124.3 (d,J=9 Hz), 119.2 (d, J=23 Hz), 116.7 (d, J=22 Hz), 105.9 (d, J=3 Hz),86.9. ¹⁹F{¹H} NMR (282 MHz): δ −113.2. Anal. Calcd. for C₄₄H₂₈F₂Ge: C,79.19; H, 4.23; Found: C, 78.83; H, 4.00.

Example 9

Formation of 1,1-Bis(thiophen-3-ylethynyl)-2,3,4,5-tetraphenylgermole(9)

Purification of (9) by column chromatography using silica gel andhexane/toluene (2:1) as the eluent yielded a yellow solid (418 mg, 70%).Yellow crystals were grown by slow evaporation from a methylenechloride/hexane mixed solvent system. M.p. 254-255.5° C. ¹H NMR (500MHz): δ 7.60 (d, J=3 Hz, 2H), 7.28-7.24 (m, 6H), 7.22-7.14 (m, 6H),7.14-7.10 (m, 2H), 7.10-7.05 (m, 6H), 6.93-6.88 (m, 4H). ¹³C{¹H} NMR(125 MHz): δ 153.1, 138.8, 138.0, 136.1, 130.9, 130.4, 130.0, 129.9,128.1, 127.9, 126.8, 126.7, 125.4, 121.9, 102.3, 85.6. Anal. Calcd. forC₄₀H₂₆GeS₂: C, 74.67; H, 4.07; Found: C, 74.88; H, 3.97.

Example 10 Formation of1,1-Bis((3-pyridinyl)ethynyl)-2,3,4,5-tetraphenylgermole (10)

Purification of (10) by column chromatography using silica gel andmethanol as the eluent yielded a yellow solid (472 mg, 60%). Yellowcrystals were grown by slow evaporation from a methylenechloride/diethyl ether mixed solvent system. M.p. 220-221.5° C. ¹H NMR(300 MHz): δ 8.76 (dd, J=2, 0.7 Hz, 2H), 8.56 (dd, J=5, 1.7 Hz, 2H),7.81 (dt, J=8, 1.9 Hz, 2H), 7.29-7.03 (m, 16H), 6.91-6.86 (m, 4H).¹³C{¹H} NMR (125 MHz): δ 153.5, 153.1, 149.5, 139.3, 138.5, 137.7,135.5, 129.9, 129.8, 128.3, 128.0, 127.0, 126.9, 123.1, 119.7, 104.0,89.7. Anal. Calcd. for C₄₂H₂₈GeN₂: C, 79.65; H, 4.46; Found: C, 79.18;H, 4.36.

Example 11 Formation of1,1-Bis((2-pyridinyl)ethynyl)-2,3,4,5-tetraphenylgermole (11)

Purification of (11) by column chromatography using silica gel andmethanol as the eluent yielded a yellow solid (447 mg, 66%). Yellowcrystals were grown by slow diffusion from a hexane/methylene chloride(2:1) mixed solvent system. M.p. 260° C. (dec). ¹H NMR (300 MHz): δ 8.59(ddd, J=4.9, 1.7, 0.9 Hz, 2H), 7.66 (td, J=7.7, 1.8 Hz, 2H), 7.54 (dt,J=7.8, 1.1 Hz, 2H), 7.29-7.19 (m, 6H), 7.15-7.02 (m, 10H), 6.90-6.84 (m,4H). ¹³C{¹H} NMR (75 MHz): δ 153.8, 150.4, 142.9, 138.9, 137.9, 136.6,135.7, 130.2, 130.2, 128.5, 128.4, 128.2, 127.1, 127.0, 124.0, 105.9,86.6. Anal. Calcd. for C₄₂H₂₈GeN₂: C, 79.65; H, 4.46; Found: C, 79.39;H, 4.91.

Example 12 Formation of1,1-Bis((diphenylphosphino)ethynyl)-2,3,4,5-tetraphenylgermole (12)

Purification of (12) by column chromatography using silica gel andhexane/toluene (2:1) as the eluent yielded a yellow solid (450 mg, 44%).Yellow crystals were grown by slow evaporation from diethyl ether. .p.154.5-156° C. ¹H NMR (500 MHz): δ 7.58-7.53 (m, 8H), 7.34-7.24 (m, 14H),7.23-7.19 (m, 4H), 7.16-7.13 (m, 6H), 7.10-7.05 (m, 6H), 6.89 (dd, J=8,1.7 Hz, 4H). ¹³C{¹H} NMR (125 MHz): δ 153.4, 138.5, 137.6, 135.7, 135.5(d, J_(PC)=6 Hz), 132.7 (d, J_(PC)=21 Hz), 130.0, 129.9, 129.2, 128.8(d, J_(PC)=8 Hz), 128.2, 127.9, 126.9, 126.8, 107.2 (d, J_(PC)=18 Hz),106.5 (d, J_(PC)=3 Hz). ³¹P{¹H} NMR (202 MHz): δ −32.2. Anal. Calcd. forC₅₆H₄₀GeP₂: C, 79.36; H, 4.76; Found: C, 79.69; H, 5.06.

Example 13 X-Ray Structure Determination

Crystals of x-ray diffraction quality were obtained by slow evaporationfrom a methylene chloride/hexane mixed solvent system for 8 and a slowevaporation of a saturated diethyl ether solution for 12. Crystals ofappropriate dimension were mounted on a glass capillary in a randomorientation. Preliminary examination and data collection were performedusing a Bruker Kappa Apex II Charge Coupled Device (CCD) Detector systemsingle crystal X-Ray diffractometer using an Oxford Cryostream LTdevice. Data were collected using graphite monochromated Mo Kα radiation(λ=0.71073 Å) from a fine focus sealed-tube X-Ray source. Preliminaryunit cell constants were evaluated with a set of 36 narrow frame scans.Typical data sets consist of combinations of ω scan frames with typicalscan width of 0.5° and exposure time of 15-20 seconds/frame at a crystalto detector distance of 4.0 cm. The collected frames were integratedusing an orientation matrix determined from the narrow frame scans. ApexII and SAINT software packages were used for data collection and dataintegration. Final cell constants were determined by global refinementof reflections from the complete data set. Collected data were correctedfor systematic errors using SADABS based on the Laue symmetry usingequivalent reflections.

Structure solution for 8 was carried out using the SIR-92 softwarepackage, and structure refinement was performed using the CRYSTALSsoftware package. Structure solution and refinement for 12 was performedusing the SHEL-XTL 97 package. The structures were solved by directmethods in the triclinic space group P1 and refined with full matrixleast-squares refinement by minimizing Σw(F_(o) ²−F_(c) ²)². Allnon-hydrogen atoms were refined anisotropically to convergence. One ofthe phenyl rings in 12 is disordered over two positions. Disorder wasresolved with 50% occupancy atoms. All H atoms were added in thecalculated position and were refined using appropriate riding models.The models were refined to convergence to the final residual values ofR₁=4.0% and wR₂=11.2% for 8, and R₁=3.9% and wR₂=13.1% for 12.

Example 14 Preparation of unsymmetrical 1,1′-substituted germoles from1-chloro-1-ethynyl-2,3,4,5-tetraphenylgermole

For the unsymmetrical 1,1′-substituted germoles, the Curtis procedurewas used to prepare a 1-chloro-1,2,3,4,5-pentaphenylgermole precursor(13). Reaction of this precursor (13) with the Grignard reagent,ethynylmagnesium bromide, afforded a1-ethynyl-1,2,3,4,5-pentaphenylgermole (14) (Scheme 2-3).

It was anticipated that the 1-ethynyl-1,2,3,4,5-pentaphenylgermole (14)would be stable enough to undergo a conventional palladium-catalyzedcross-coupling reaction. Reactions between terminal alkynes and aryliodides appear to be quite tolerant of polar functional groups such asamines, hydroxyls, and esters. Such groups are extremely difficult tointroduce by any other synthetic means, but are highly desirable forsensory applications and biological probe applications for which similarsiloles have been used. Unsymmetrical 1,1′-substituted germoles areexpected to exhibit significantly higher quantum efficiencies in thesolid state than their symmetrical analogs. Related siloles differing in1,1′-substitution exhibited higher solid state quantum efficienciescompared to the symmetrical 1,1-substituted siloles which was attributedto a higher degree of difficulty in packing compactly in the solidstate.

Example 15 Preparation of 2,7- and 3,6-disubstituted Germafluorenes

Germafluorenes were investigated to gain insight into changes of theoptical and electrical properties upon expanding the germole core. Group14 fluorenes such as sila- and germafluorene were of particular interestas they are increasingly being used as key building blocks in conjugatedpolymers. The optical and electronic properties of these n-conjugatedmaterials are intricately tied to their electronic structures which canbe tuned by incorporating functional groups, fused aromatic rings, andbridging heteroatoms. In an effort to improve upon these materials,synthetic methods for the preparation of germafluorenes with broadstructural variations that satisfy requirements for conjugation controlneed to be developed. The current limited numbers of studies usinggermafluorenes have illustrated the promise of these heterocycles forelectronic applications; thus, further investigations of the propertiesof various germafluorenes were required for the development of advancedmaterials.

Many of the structural prerequisites for AIE(E) molecules can be readilyincorporated into germafluorenes at several of the sites of substitutionto minimize the problems associated with the aggregation that isnotorious for rendering luminophors ineffective for solid stateapplications in electroluminescent devices. The fluorene central coreprovides three sites for substitution that would allowstructure-property investigations: the exocyclic positions (9,9=R)directly attached to the germanium as well as those meta (2,7=R1) andpara (3,6=R2) to the germanium center.

Reported herein is the preparation of a series of 2,7- and3,6-disubstituted germafluorenes. This example relates to the syntheticmethods used to prepare the different dihalo precursors andfunctionalized monomers.

A 2,7-dibromo-3,6-dimethoxy-9,9-germafluorenes building block wasinitially selected as it was thought that this heterocycle wouldbroadened the scope of 2, 7-functionalized monomers. Not only does themethoxy substituent serve as an ortho/para directing group as well as aNMR marker, but it serves as a site for substitution to extend theπ-conjugated system of the germafluorene. Using a nickel catalyzedcross-coupling reaction with phenylmagnesium bromide, under conditionsreferred to as Dankwardt's conditions, the methoxy substituent can bereplaced by a phenyl ring.

The preparation of the 2,7-dibromo-3,6-dimethoxy-9,9-germafluorene (16)was accomplished through three separate reactions by utilizing amodified procedure originally published by Huang. The formation of thetetrahalobiphenyl was crucial to the overall success of this route since9-heterofluorenes cannot withstand typical brominating or iodinatingmethods and are prone to cleavage; therefore, it was necessary tohalogenate the biphenyl prior to the ring closing step. The startingmaterial, o-dianisidine, was commercially available and underwent adiazotization reaction followed by a modified Sandmeyer reaction toyield the 4,4-dibromo-3,3-dimethoxybiphenyl. The4,4-dibromo-3,3-dimethoxybiphenyl was then iodinated using aniodine/potassium iodate system to yield the6,6-diiodo-4,4-dibromo-3,3-dimethoxybiphenyl. Using the reactivitydifference of iodo and bromo substituents towards n-butyllithium, theiodo substituents selectively underwent a halogen/metal exchangereaction followed by ring closure with a germanium reagent,dichlorodiphenylgermane. Simple aryl substituents such as phenyls wereinitially selected as the substituents at the 9,9-positions because theyprovide the steric congestion necessary to disrupt the packingarrangement of AIE(E) molecules and should aid the thermal stability ofthe molecules by increasing the melting points.

The preparation of a 3,6-dibromo-9,9-germafluorene (20) was accomplishedthrough four separate reactions by utilizing a modified procedureoriginally published by Holmes. Like the earlier synthetic pathway forthe 2,7-dibromo-3,6-dimethoxy-9,9-germafluorene (16), it was necessaryto construct the tetrahalobiphenyl precursor prior to the formation ofthe germafluorene. However, in this case, a suitable biphenyl was notcommercially available and had to be prepared. The commerciallyavailable 1,2-dibromo benzene was selected as the starting reagent as itcould be coupled to yield 2,2′-dibromobiphenyl which would serve as theorganic framework for the heterocycle but required conversion to the2,2′-diiodo analog. A second halogen/metal exchange reaction of2,2′-dibromobiphenyl followed by quenching with iodine gave therequisite 2,2′-diiodobiphenyl that then was then brominated utilizing aniron catalyst to yield the key tetrahalobiphenyl precursor. Thisparticular route of substitution was necessary in order to obtain thebiphenyl with the iodo substituents in the 2,2′-positions so that aselective halogen/metal exchange between the iodo substituents andn-butyllithium would yield the ring closed product,3,6-dibromo-9,9-dibenzogermafluorene (20).

Synthetic procedures were also developed that allowed covalentdecoration of discrete germafluorene monomers with a variety ofsubstituents that were anticipated to exhibit high efficiencyluminescence particularly in the solid state. Although processes such asdonor-acceptor push-pull interactions, J-aggregate formation, or twistedintramolecular charge transfer (TICT) between polar functional groups donot activate the AIE(E) effect, incorporation of functional groups mayallow control of the emission color. Therefore, a series of substituentswas selected, which were known to exhibit a particular emissionwavelength in siloles, for incorporation into the2,7-dibromo-3,6-dimethoxy-9,9-germafluorene (16) and3,6-dibromo-9,9-germafluorene (20). The 4-ethynyl-trifluorotoluene waspurchased commercially while the other three substituents,4-(ethynylphenyl)diphenylaniline, 9-(4-bromophenyl)-9H-carbazole, and2-(4-bromobenzylidene)malononitrile, were prepared according to knownliterature procedures. It was anticipated that these discrete monomersmay perform as well or better than their polymeric counterparts.

These substituents were incorporated into the dihalo precursors usingclassical Sonogashira cross-coupling reactions. The2,7-dibromo-3,6-dimethoxy-9,9-germafluorene (16) or3,6-dibromo-9,9-germafluorene (20) were coupled to the prepared terminalalkynes (4-ethynyl-trifluorotoluene and 4-(ethynylphenyl)diphenylanilinein an amine and THF mixed solvent withtetrakis(triphenylphosphine)palladium(0) and copper(I) iodide asco-catalysts. Therefore, in hopes of improving the efficiencies of thesereactions, the bromo substituents were replaced by an ethynyl linkagesuch that the coupling could now result in the coupling of acarbon-carbon bond instead of a carbon-bromine bond.

Example 16 Preparation of Fluorescein-Based Molecules ContainingGermanium

This class of heterocycles was prepared using modifications of aprocedure which was originally developed for silicon. The entiresynthetic pathway required the sequential preparation of six precursorcompounds in order to obtain the final fluorescein derivative (26) whichcould potentially serve as the building block for a series of novelgermanium heterocycles that are expected to emit in the red region ofthe electromagnetic spectrum.

In order to synthesize the germaanthrone (22), it was first necessary toprepare the organic framework which would eventually undergo ringclosure to obtain the target compound (21). Since none of the precursorcompounds for this synthetic pathway were available commercially, thismultistep process began with the protection of 3-bromoaniline with allylbromide to form the monomer 3-bromo-N,N-diallylaniline. Thediallylaniline then underwent an industrial condensation reaction withformaldehyde to yield the diaryl,bis(2-bromo-4-N,N-diallylaminophenyl)methane (21). The diaryl methane(21) represented the completed organic skeleton necessary for ringclosure with a substituted germanium dichloride. From this point forwardin the synthetic pathway, the substituents on the germaanthrone (22)were manipulated to transform this key compound into the finalfluorescein form. The initial manipulation involved apalladium-catalyzed de-allylation reaction to restore the amino groupsforming a diamino-germaanthrone (23). The next manipulation is the mostimportant since it is at this point that the germaanthrone (23) is to beconverted to the phenol derivative making the final fluorescein-basedstructure possible.

The dihydroxy-germaanthrone (24) can be obtained by conversion to atert-butyldimethylsilyl ether (25) with tert-butyldimethylchlorosilane(TBDMS) using imidazole as a catalyst. This process, which may proceedthrough a N-tert-butyldimethylsilylimidazole intermediate, affords ahighly stable protecting group for alcohols. This ether can then besafely coupled with a variety of lithiated aryl substituents at the Rposition to generate (26). Additionally, the hydroxyl (OH) group on thefluorescein analog (26) can serve as an additional site of substitutionto generate other unique derivatives.

While the disclosure has been described in connection with specificembodiments thereof, it will be understood that the inventive device iscapable of further modifications. This patent application is intended tocover any variations, uses, or adaptations of the disclosure following,in general, the principles of the disclosure and including suchdepartures from the present disclosure as come within known or customarypractice within the art to which the disclosure pertains and as may beapplied to the essential features herein before set forth.

What is claimed is:
 1. A TLC plate for detection of organic vaporcompounds comprising a coating layer comprising a compound having theformula (I)

wherein R₁ and R₂ may be independently selected from optionallysubstituted aryl, optionally substituted heteroaryl, and optionallysubstituted alkynyl.
 2. The TLC plate of claim 1, wherein R₁ and R₂ maybe selected independently from the group consisting of

wherein X═H, CF₃, OCF₃, CH₃, OCH₃, Ph, OPh and derivatives thereof. 3.The TLC plate of claim 1, wherein R₁ and R₂ are each


4. The TLC plate of claim 1, wherein R₁ and R₂ are each


5. The TLC plate of claim 1, wherein R₁ and R₂ are each


6. The TLC plate of claim 1, wherein R₁ and R₂ are each


7. The TLC plate of claim 1, wherein at least one of R₁ and R₂ isselected from a substituted aryl or a substituted heteroaryl, andwherein the other one of R₁ and R₂ may be independently selected from anon-substituted aryl, a substituted aryl, a non-substituted heteroaryl,a substituted heteroaryl, a non-substituted alkynyl, or a substitutedalkynyl, and wherein R₁ and R₂ are different.
 8. The TLC plate of claim7, wherein one of R₁ or R₂ is a substituted aryl and the other one of R₁or R₂ is a non-substituted alkynyl or a substituted alkynyl.
 9. The TLCplate of claim 7, wherein one of R₁ and R₂ is


10. The TLC plate of claim 7, wherein R is selected from the groupconsisting of CH₃, CF₃, OCF₃, OCH₃, N(CH₃)₂, and C(CH₃)₃.
 11. The TLCplate of claim 7, wherein the aryl or heteroaryl is selected from thegroup consisting of

wherein X is selected from the group consisting of H, CF₃, OCF₃, CH₃,OCH₃, Ph, OPh and derivatives thereof.
 12. A compound having the formula(II)

wherein R₁ and R₂ may be independently selected from the groupconsisting of aryl, alkyl, halide, alkynyl, and asymmetric derivativesthereof with two different groups at the Ge-center; wherein R₃ and R₆may be independently selected from the group consisting of Y and

wherein R₄ and R₅ may be independently selected from the groupconsisting of OCH₃;

 and Y; and wherein Y is H,

 wherein Z is F, CH₃, or OCH₃;

 wherein X is H, CF₃, OPh, CH₃, Ph, OCH₃ or OCF₃; or

 wherein R is aryl, alkenyl or alkynyl.
 13. A compound having theformula (III)

wherein R₁ and R₂ may be independently selected from the groupconsisting of aryl, alkyl, halide, alkynyl, and asymmetric derivativesthereof with two different groups at the Ge-center; wherein R₄ and R₇may be independently selected from the group consisting of ═O, —OH, andOSi(CH₃)₂[C(CH₃)₃] hydroxyl or carbonyl amine and ether derivatives;wherein R₅ and R₆ are H; and, wherein R₃ is Y, ═O, C₆H₅, p-CH₃C₆H₅,p-CH₃OC₆H₅ or

wherein Y is

 wherein Z is F, CH₃ or OCH₃;

 wherein X═CF₃, OPh, CH₃, Ph, OCH₃ or OCF₃;

 wherein NR₂═NH₂, NMe₂ or NEt₂ and Z=Me, CO₂H, C(═O)H, or CO₂Me;

wherein R is alkyl and Z=Me, CO₂H, C(═O)H, or CO₂Me; or,

 wherein R is alkyl or H.
 14. The compound of claim 13 having theformula (III-A)

wherein R₁ and R₂ may be independently selected from the groupconsisting of aryl, alkyl, halide, alkynyl, and asymmetric derivativesthereof with two different groups at the Ge-center; wherein R₃ isselected from the group consisting of C₆H₅, p-CH₃C₆H₅, p-CH₃OC₆H₅, andanother substituted aromatic substituent; and, wherein R_(q) is H oranother substituted aromatic substituent.
 15. A compound having theformula (IV)

wherein R₁ and R₂ may be independently selected from the groupconsisting of aryl, alkyl, halide, alkynyl, and asymmetric derivativesthereof with two different groups at the Ge-center; wherein R₃ and R₆may be independently selected from the group consisting of H, Cl, Ar, Yand

wherein R₄ and R₅ may be independently selected from the groupconsisting of H, aryl, I, Br, Y or

 and wherein Y is

 wherein Z is F, CH₃ or OCH₃;

 wherein X is CF₃, OPh, CH₃, Ph, OCH₃ or OCF₃;

 or wherein R is aryl, alkenyl or alkynyl.
 16. The compound of claim 15having the formula (IV-A)

wherein R₇ and R₈ may be independently selected from the groupconsisting of aryl, alkyl, halide, alkynyl, and asymmetric derivativesthereof with two different groups at the Ge-center.
 17. The compound ofclaim 15 having the formula (IV-B)

wherein R₉ and R₁₀ may be independently selected from the groupconsisting of aryl, alkyl, halide, alkynyl, and asymmetric derivativesthereof with two different groups at the Ge-center.